About unsolved Riddles with the extinct Animals

(last update: 3. Dec 1999)

First, I'm physicist and not biologist and therefore
no real expert. Despite this, in the following I try to present some open
questions with the fascinating reptiles and the current discussioned aspects,
enriched with some own opinions.

Some matters will probably never resolved completely, but others may
very well. Keep this in mind...

Why they vanished at all?

The most discussed problem is the extinction 65 million years ago, in which
not only dinosaurs, but also pterosaurs and whale like reptiles (Ichthysauria
and others) alongside with some other groups of animals were wiped out.
At this time dinosaurs ruled the continents for more than 150 million years
(!) and it is really hard to comprehend, why not even a single species
of them could survive this mass extinction; in the 150 million years before
there occured also catastrophical developments and events from time to
time, no way threatening the reptile fauna in a similar manner.

For me, a combination of several factors seems to be most likely as
explanation. A general tendency of global cooling may have millions before
the extinction made the dinosaurs less successful and frequent as before,
giving warm blooded animals like birds and mammals better chances to compete
with the dominating reptiles. Than a catastrophical volcanism in the Indian
Dekkan-Trapps occured, further worsening in hundred thousands of years
the life conditions --- further cooling, air polluting, affecting the plants
and so on. Finally a 10 km meteorid impacted at the Yucatan peninsula,
not only creating the about 200 km diameter crater of Chicxulub, but also
devastating finally an already damaged biosphere in an incredible harsh
manner, killing many animals off right through fireball, shockwaves in
the Earth crust and so on and creating an "impact winter", later followed
by a soaring phase. Eventually the impact may have also worsened the Dekkan
volcanism. The warm-blooded animals like birds and mammals may have gained
their surviving by their lower sizes (less vulnerable for mechanical shocks)
and better ability for temperature regulation... But the details are hard
to unveil completely, due to the long time elapsed since then. For example,
representative fossils of dinosaurs are hard to find in sufficient numbers
for statistical purposes, when short time developments and/or events are
to be scrutinized.

How intelligent they were?

You may have heard or read about the tiny brain for example of Stegosaurus.
But this is somewhat a misinterpretation, slightly resembling to insects
this jurassic dinosaur had also some massive sub brain like knots in his
nervous system and may be therefore better developed in this respect as
thought before.

Indeed, most dinosaurs had clearly less well developed brains than todays
average mammals. But there were differences and a general tendency for
advanced brain development especially at the end of the cretaceous period,
immediately before their mass extinction. The groups with most intelligence
in this era were the dromaeosauria, to which belong the famous Deinonychus
as well as the now infamous Velociraptor (do you remember "Jurassic Park"?
- I don't like the presentation of meat eaters as beasts with unbridled
bloodlust), and even more the troodontids, also theropods and therefore
meat eaters, and indeed dinosaurs despite the somewhat unusual name for
such a species. This Troodon had a brain size compared to its human comparable
height, which is similar to modern mammals. You may speculate, what could
have happened in the long run, if these species Troodon had survived the
mass extinction?

What about Body Temperatures?

First, cold blooded and warm blooded are somewhat inadequate terms. There
are better ones, but for now I will stick to them. What is really meant,
is the temperature kept in a small interval at a certain value (warm blooded),
or is it varying according the environmental temperature (cold blooded),
therefore often (but not always!) lower.

Today this question is broken down into several groups of the dinosaurs.
For example the giant sauropods like brachiosaurus, apatosaurus and diplodocus
may have kept their temperature constant by their sheer size without many
active regulation mechanisms. This possibility is due to the very low surface
to volume ration with such giant animals. This is a simple physical effect.

Some of the less sized theropods may have had similar to birds some
feathers or other protection mechanism against strong cooling and an active
metabolism, capable to heat the body considerable.

The biggest problem may be the larger theropods, mainly the carnosaurs.
There the question is vastly open, related with the living style of these
animals, of which the Tyrannosaurus Rex is the most popular, the most advanced
and one of the biggest.

A new aspect was revealed a short time ago: it seems, that at least
some theropods had some sort of "turbo" or "afterburning" capabilities,
low energy consuming at most times and resembling "modern" reptiles, which
are generally far less developed than the dinosaurs were, and than for
short times activating this extra energy consumption while hunting or eventually
even for fighting against rivals of the own species (they were probably
similar "unfriendly" to each other, as many modern mammal meat eaters).

Generally speaking, together with their well moving capabilities ---
unlike todays reptiles as crocodiles and lizards --- most of them may have
been far more active, than previously thought.

Carnosaurs and Tyrannosaurus Rex...

One of the most hot debated topics is the nourishing behaviour of these
animals, especially of the famous Tyrannosaurus Rex. There are two opposite
opinions: some think, that these theropods were to heavy, to slow and too
much demanding for food to move quickly around, and therefore were mainly
eating cadavers of dead dinosaurs alongside with others. Others think,
that the horrible equipment of these animals with teeth and claws at the
end of their short arms forces the conclusion, that they were actively
preying. A third group (I share this last view) think, that they were similar
the bigger meat eating mammals of today: bears and big cats. Therefore
they may have hunted actively at good occasions and then also eating dead
animals, eventually also robbing other hunters their prey, and even killing
big plant eaters, when it was feasible. This riddle may be solved with
the decades to come... As mentioned above, this topic is strongly related
to the question, if these animals were warm blooded. If yes, the active
preying picture is far more probable.

Caring for minor Ones?

Already famous is the Majasaura: resembling colonies of birds, they built
giant arrays of nests and caring for the young Majasaura, after they hatched
from the eggs, arranged in the center of the nest. Similar to today colony
breeding birds, this may have offered the usual advantage: better guarding
and protection against meat eaters.

Maybe this was more widespread then previously thought: even sauropods
may have helped the younger members to defend against carnosaurs and dromaeosaurids.
This leads directly to the next topic:

Living in Groups

This was probably a common behaviour of many species of them. So it is
thought about sauropods, the Iguanodon, ceratopsids like the Triceratops,
the Ornithomimus and even with many dromaeosaurs. With the last, the background
is of course contrary: as shown in "Jurassic Park", these probably hunted
similar as wolves today even plant eaters bigger than themselves; and these
theropods were really quick moving reptiles. Nearly for sure is this behaviour
for the famous Deinonychus, which preyed in a group on an Iguanodon. But
not all behaved this way, the bigger theropods like carnosaurs were probably
as much for themselves as most todays bigger mammal meat eaters (like bears
or tigers). In some cases, like the sauropods, the evidence for building
groups is not totally clear, I have to remark.

Reproduction on a "big scale"

It's considered as probable, that the number of eggs of dinosaurs was comparable
to todays crocodiles. But before laying eggs, they had to do a job --- the
usual one. Now imagine these giant animals, especially the big sauropods
like Brachiosaurus. Because these heavyweights were not able to carry there
body on for example the two front legs solely and walked generally with three
legs on the ground at any time, the pure mechanical problem of the huge load
on their bones must have been important. Anyway, the male had to put himself
onto the female, nearly doubling the load, severing the light, but strong
bones of the female to break. Even with other, not so heavy species, like
Ankylosaurus, this remains an open question: how they did it get worked?
(The Ankylosaurus was armored totally, offering difficulties for that reason.)

Colors, Voices and so on...

Extremely speculative is the color of the dinosaurs. These features don't
conserve at all and so do also the eyes, which could give hints. So only
probability analyses remain as feasible way, to make some guesses about
it. But it is not more, and unless the highly speculative project like
"Jurassic Park" succeeds in rebuilding exact "copies" of dinosaurs, this
will be impossible to tell.

The voices are often also speculative, but in some cases there are hints
in the skeletons, the only parts, which conserve well. So Saurolophus and
some related species had unusual elongated or other deviating head shapes,
which seems to make likely the usage as acustical tools for loud noises
of what type ever. But generally there is not much more known about this
topic, than about the colors.

Birds --- the Offspring of the Dinosaurs (?)

Most experts agree nowadays, that the birds emerged from lower sized dinosaurs
like the chicken sized Compsognathus. But the direct evolution into the
famous Archaeopteryx may not have been as easy as straight at thought decades
ago. There are evidences for both types of sidelines and several splittings
into birds or bird resembling animals, making a real confusing picture
at now, also in respect of evolution time. And the way, in which they acquired
the flying and feathers, is also not as clear, as the experts wish. These
features may have occured already in their dinosaur state, as well as already
as early birds; the difficulties to classify intermediate forms like Archaeopteryx
in every aspect of their body and the always difficult derivable behaviour
make it no more easy. One of the not so many confirmed facts: birds were
already present in wide areas in the late cretaceous period, existing while
dinosaurs dominated the land and the flying pterosaurs were also widespread.